As a result of industrial and/or purification treatments, large quantities of sludge solutions are produced, containing solid material that needs to be disposed of or reused.
These solutions may contain sand, soil, cellulose, residues of material deriving from working with or washing machinery or tanks, or biological decantation sludge.
The bulk and the weight of similar waste materials or materials for reuse are considerable; it has therefore been necessary to study solutions for reducing the volume and the weight so as to be able to transport and store them at the lowest possible cost while they await final disposal or, as the case may be, reuse for different purposes.
The solution currently adopted to obviate this problem is to reduce the water content of the sludge material.
There are various methods and techniques used for dehydrating the sludge, which undergoes treatments of physical, chemical, mechanical or thermal type.
Some of the treatments used, for example, are drying, centrifuging, depressurising or again pressing.
One technique in current use involves filling special moulds under pressure with the sludge material in order to force the water out through filtration fabrics, to reduce the water content.
This process is long and laborious because only a limited and predetermined quantity of sludge can be treated in each cycle. In fact, it is necessary to load the sludge which is to be dehydrated, and start up the pressurising machinery. In a given period of time it is possible to process only a small quantity of sludge residue.
The efficiency of this process, furthermore, is not ideal, since it produces dehydrated sludge with a percentage of dry matter (d.m.) which is still fairly low, around 30-33%.
The cycle thus entails various interruptions of the dehydrating process, which enables only a small quantity of sludge material to be treated per unit of time, besides entailing high processing and maintenance costs. Alternatively, the sludge to be treated is transported on belts and run through rollers, which press the sludge, reducing the moisture content. Besides not being particularly efficient, these machines are extremely bulky and need to be attended.
Alternatively, centrifuging can be used, but this yields a d.m. content which is still very low, 22-25% d.m.